Stable surface-based turbulent layer during the polar wnter at Dome C, Antarctica: sodar and in situ observations

An experiment to investigate atmospheric turbulence was performed at Concordia station (Dome C, Antarctica) during winter 2012, finding significant turbulence in a near-surface layer extending to heights of a few tens of metres, despite the strong stable stratification. The spatial and temporal behaviour of thermal turbulence is examined using a high-resolution sodar, starting from the lowest few metres with a vertical resolution better than 2 m. Sodar observations are complemented by in situ measurements using a weather station and radiometers near the surface, temperature and wind-speed sensors at six levels on a 45-m tower, and radiosondes. The depth of the surface-based turbulent layer (SBTL) at Dome C during the whole winter is directly measured experimentally for the first time, and has an average depth of ? 23 m, varying from a few to several tens of metres, while the inversion-layer depth ? 380 m. Relationships between the depth of the SBTL and atmospheric parameters such as the temperature, wind speed, longwave radiation, Brunt-Väisälä frequency and Richardson number are shown. The SBTL under steady weather conditions is analyzed and classified into three prevailing types: 1) a very shallow layer with a depth < 15 m, 2) a shallow layer of depth 15-70 m with uniform internal structure, 3) a shallow layer of depth 20-70 m with waves. Wave activity in the SBTL is observed during a significant portion of the time, with sometimes regular (with periodicity of 8-15 min) trains of Kelvin-Helmholtz billow-like waves occurring at periods of 20-60 s, and lasting several hours.